1. Field of the Invention
The present invention pertains to the field of advanced sporting equipment design and in particular to the design and operation of a golf club head system for control of the impact between a club head and a golf ball.
2. Background Art
The present invention pertains to achieving an increase in the accuracy and distance of a golf club(e.g., a driver) through the application of controls techniques and actuation technology to the design of the club. There have been many improvements over the years which have had measurable impact on the accuracy and distance which a golfer can achieve. These have typically focused on the design of passive systems; those which do not have the ability to change any of their physical parameters under active control during the swing and in particular during the impact event with the golf ball. Typical passive performance improvements such as head shape and volume, weight distribution and resulting components of the inertia tensor, face thickness and thickness profile, face curvatures and CG locations, all pertain to the selection of optimum constant physical and material parameters for the golf club. The present invention pertains to the development of an active system where critical parameters of the golf club and head (for example surface position/shape/curvature or effective coefficient of friction, or face stiffness) can be selectively controlled in response to the actual state of the physical head-ball system. Such states can be head velocity, impact force, intensity, impact duration and timing, absolute location of the head or relative location of the ball on the face, orientation of the head relative to the ball and swing path or parameters, physical deformation of the face, or any of numerous physically or electrically measurable conditions.
The present invention relies on the field of controls technologies and in particular structural or elastic system actuation technologies and control algorithms for such systems. See for example: Fuller, C. R. et al., Active Control of Vibration Academic Press, San Diego, Calif. 1996. A particular embodiment of one controlled system relies on friction control using ultrasonic vibration (Katoh). An alternate embodiment of one controlled system relies on changing the effective stiffness of the face to control impact with the ball. The present invention also relies on the concept of piezoelectric energy harvesting and/or simultaneous energy harvesting from and actuation of mechanical systems. Piezoelectric energy harvesting is described in the following U.S. Pat. Nos. 4,504,761; 4,442,372; 5,512,795; 4,595,856, 4,387,318; 4,091,302; 3,819,963; 4,467,236; 5,552,657; and 5,703,474.
The impact between the ball and the head can be interpreted in terms of the idealized impact between two elastic bodies each having freedom to translate and rotate in space i.e. full 6 degrees of freedom (DOF) bodies, each having the ability to deform at impact, and each having fully populated mass and inertia tensors. The typical initial condition for this event is a stationary ball and high velocity head impacting the ball at a perhaps eccentric point substantially on or substantially off the face of the club head. The impact results in high forces both normal and tangential to the contact surfaces between the head and the ball. These forces integrate over time to determine the speed and direction, forming velocity vector and spin vectors of the ball after it leaves the face, hereafter called the impact resultants. These interface forces are determined by many properties including elasticity of the two bodies, material properties and dissipation, surface friction coefficients, body masses and inertia tensors.
Some of these properties and conditions of the face can be actively controlled during the impact resulting in some measure of control over the impact resultants. For example, in a specific embodiment, the surface can be ultrasonically vibrated under some predetermined condition so as to create an effectively lower friction coefficient between the ball and the face resulting in decreased spin rates and longer flight of the ball when a trigger condition is present. One such trigger condition might be high head ball impact forces (and large face deformation), indicating a high velocity impact where too much spin could create excess aerodynamic lift producing a decreased flight distance.
In another embodiment, the position and/or orientation of the face can be actively controlled relative to the ball and the body of the club under some predetermined condition so as to create a better presentation of the face to the ball for more accurate ball flight or to reduce side spin by counteracting club head rotation during eccentric impact events. One such triggering condition might be highly eccentric impact events (off center hits) that can be detected by deformation sensors on the face or angular acceleration sensors in the body. Such sensor signals could be processed to determine the necessary motion of the face to compensate and correct the resulting ball flight.
In another embodiment, the effective stiffness of the face during impact can be controlled so as to produce a more desirable impact event. For example, the system can be designed to make the face stiffer during a hard impact and make the face softer during a less intense impact so as to tailor the face behavior under the impact loads to the particular event. This can be accomplished by, for example, shorting or opening the leads of a piezoelectric transducer which has been surface bonded or otherwise mechanically coupled to a face. The piezoelectric is softer (low modulus) when it is electrically shorted and stiffer (high effective modulus) when it is open circuited. A sensor attached to the face can measure a quantity proportional to impact intensity (e.g., face deflection, face strain, head deceleration etc). In the “hard” hit case, the normally shorted piezoelectric can be open circuited to make the face stiffer, while softer hits result in the circuit leaving the piezoelectric in the short circuited condition and therefore less stiff.
The trigger can be provided by an external sensor or by the actual piezoelectric transducers bonded to the face itself by triggering off of the current or voltage level achieved on the transducer prior to the triggering event. As an example, circuitry for using the piezoelectric element as a charge sensor can be attached to the transducer leads. When the charge reaches a critical level a circuit can be triggered which disconnects the leads from the circuitry effectively enforcing the open circuit condition.
A critical element of the ability to control the ball-head impact is the ability to actuate the system in a beneficial manner. Since the head and ball are a mechanical system, this entails the application of some force or thermal energy to the system so as to create a change in some mechanical physical attribute. The present invention pertains principally to mechanical actuation techniques.
U.S. Pat. No. 6,102,426 to Lazarus, et. al, discloses the use of a piezoceramic sheet on a ski to affect its dynamic performance such as limiting unwanted vibration at higher speeds or on irregular surfaces. The disclosure mentions the application to golf clubs to dampen vibrations or alter shaft stiffness or “to affect its head”.
U.S. Pat. Nos. 6,196,935, 6,086,490 and 6,485,380 to Spangler et. al, disclose the use of piezoceramic sheets on golf clubs to alter stiffness and to effect a dampening of vibration. FIG. 9G illustrates the placement of piezo elements on a golf club head to capture strain energy to be dissipated in a circuit for a dampening effect.
U.S. Pat. No. 6,048,276 to Vandergrift relates to the use of piezoelectric devices to stiffen the shaft of a golf club after capturing energy from the swinging and flexing of the shaft.
The issue of reducing friction using ultrasonic vibration is discussed by Katoh in an article entitled “Active Control of Friction Using Ultrasonic Vibration” Japanese Journal of Tribology Vol. 38 No. 8 (1993) pp 1019-1025. See also K. Adachi et al “The Micromechanism of Friction Drive with Ultrasonic Wave”, Wear 194 (1996) pp 137-142.